I. Field of the Invention
The present invention relates generally to fuel cells and, more particularly, to a fuel cell with an improved fuel cell shutdown.
II. Description of Related Art
Although different types of electrical energy storage devices may be utilized for powering electric motor vehicles, there has been an increased interest in the use of fuel cells to provide the electric power for such electric vehicles. Such fuel cells contain both a cathode and an anode, each of which has a gaseous flow path. A gaseous fuel, such as hydrogen, is coupled to the flow path of the anode while a reactant gas, such as air containing oxygen, flows through the cathode flow path. An electrolyte is positioned in between the anode and cathode flow paths while the anode and cathode are connected to an electrical load, such as a battery.
In operation, the hydrogen flow through the anode flow path disassociates the hydrogen into protons and electrons. The protons conduct through an electrolytic membrane directly to the cathode while the electrons travel through the electric load. At the cathode, the oxygen molecules combine with the disassociated hydrogen to form water. Consequently, the exhaust or outflow from the cathode flow path comprises primarily nitrogen and water vapor.
In the previously known fuel cells, in order to shut down the fuel cell, the supply of oxygen and air to the fuel cell anode and cathode flow path was terminated. While termination of both the hydrogen and oxygen to the fuel cell terminates the production of electrical power from the fuel cell, an electrical charge remains on the fuel cell membrane. Over time the charge on the fuel cell membrane following fuel cell shutdown may result in degradation of the fuel cell.
One way to prevent degradation of the fuel cell from the charge remaining on the fuel cell membrane following shutdown is to blow out or purge the anode flow path during the fuel cell shutdown. A bottle of compressed helium or compressed nitrogen may be selectively fluidly connected to the anode flow path in order to purge the flow path. The use of such stored nitrogen or helium, however, is disadvantageous where the fuel cell is used in a motor vehicle since the purged gas must be replenished periodically.